モンテカルロ法で Pi を計算

PiTest.java

package test;

import java.util.concurrent.Callable;
import java.util.concurrent.ThreadLocalRandom;
import java.util.stream.IntStream;

public class PiTest {
    public static void main(String[] args) {
        final int N = 100_000_000;
        task("calcPi(for loop)", () -> calcPi(N));
        task("calcPi(Stream)", () -> calcPiStream(N));
        task("calcPi(Stream + Parallel)", () -> calcPiParallel(N));
    }

    public static void task(String taskName, Callable<Double> callable) {
        long t0 = System.currentTimeMillis();
        double result = 0;
        try {
            result = callable.call();
        } catch (Exception e) {
            e.printStackTrace();
        }
        long t1 = System.currentTimeMillis();
        System.out.printf("%30s\t%18.16f\t%4d msecs\n", taskName, result, t1 - t0);
    }
    public static double calcPi(int num) {
        int count = 0;
        for (int i = 0; i < num; i++) {
            if (calc()) {
                count++;
            }
        }
        return (double)count / num * 4D;
    }

    public static double calcPiStream(int num) {
        long count = IntStream.rangeClosed(1, num).filter(i -> calc()).count();
        return (double) count / num * 4D;
    }

    public static double calcPiParallel(int num) {
        long count = IntStream.rangeClosed(1, num).parallel().filter(i -> calc()).count();
        return (double) count / num * 4D;
    }

    public static boolean calc() {
        double x = ThreadLocalRandom.current().nextDouble();
        double y = ThreadLocalRandom.current().nextDouble();
        return (x * x + y * y) <= 1;
    }
}